By default, GTA SA has unique cop model for each city. However, there's only one cop biker for whole state. It has a bit of nonsense, as his model name apparently tells that is a LS biker. Also, Rockstar left in gta3.img two fully usable models of bikers for SF and LV.

Why not make them usable? This mod (or rather, this plugin) adds them to the city, as they should be placed, according to their names.

Believe me or not, that mod doesn't spawn cops by itself, only hacks the EXE routines. However, you even don't have to believe me, as mod is open sourced

Put cbo.cs in GTA San Andreas\CLEO directory and peds.ide in GTA San Andreas\data directory to install the mod.If your peds.ide file is modified, add mod lines by yourself by pasting them below #---ADD NEW PEDS HERE line. You have to paste these two lines:

Fenton

I just suggesting, Desert Sheriff should be added in Desert because originally Desert sheriff were placed in desert but they're replaced by Country Sheriff instead, I don't think there is a mod adding Desert Sheriff to Desert